This is easily Reynolds' weakest novel to-date. It opens with one of Neal Stephenson's favourite technical crimes - a protagonist switch. Grrr! It would have been more difficult to pull off but the novel could have opened with the intended main protagonist finding an angel on his pathology bench. Instead there is a long scene from the point of view of two characters who are never heard from again - and you know from the outset that they are going to disappear once they've delivered the angel. So, not a good start.

A chase ensues not too long after but I had an odd reaction to it; I felt like I was reading a distillation of the generic "hero and heroine on a train are chased by pursuers intent on their murder" scene from umpteen Hollywood movies. I suppose it just felt old hat.

Things get more interesting later, but then airships turned up and I spent considerable time trying to get Philip Reeves' Mortal Engines books out of my head. I wasn't really successful until the approaching denouement. Then the denouement failed to explain enough of what had been going on. Now, Reynolds routinely ends matters with revelations of bigger mysteries and unexplored realms, but this time too many things were left unresolved for my taste - and sequels are not Reynolds' favourite things.

There is much to admire in terms of the SF setting and characters but this is a very disappointing effort, particularly coming immediately after the excellent House of Suns.

PS. Did I mention that there's a guy who's had his memories over-written - again!